The invention relates to a road construction machine, a leveling device, and a method. This application is a continuation of U.S. Ser. No. 13/098,798 now U.S. Pat. No. 8,308,395, which is a continuation of U.S. Ser. No. 12/225,792 now U.S. Pat. No.7,946,788. Which is a 371 of PCT/EP 2007/053590
It is already known for road milling machines to integrate a leveling device by means of which it is to be ensured that an even milled surface can be produced.
The milling depth control system is designed in such a fashion that different sensors can be connected. Among others, the sensors used include, for example, wire-rope sensors, ultrasonic sensors and slope sensors.
A wire-rope sensor is mounted at the side plates (edge protection) next to the milling drum and thus scans the reference surface, in this case the road surface, very precisely. The ultrasonic sensor operates in a non-contact fashion and is therefore not subject to any mechanical wear and tear. It can be used in a variety of ways as it can be attached in different positions on the machine.
If a defined cross slope is to be produced, a slope sensor can also be used which is integrated into the road milling machine.
The known milling depth control system can be provided with two independent control loops. A controller is provided in each control loop to which the sensors can be connected via plug-in connectors. For example, either two height sensors are provided, or one height sensor in combination with one slope sensor.
It is unfavorable in the state of the art that the frequent change between the many different sensors, which is necessary for application-related reasons, is not possible without an interruption of the milling operation and without negative influences on the work result. To change the current sensor, the automatic mode of the control system needs to be left first as there is merely one controller, or merely one indication and setting device for set values and actual values per controller respectively. The new sensor can then be selected, and the desired set value can be set before it is possible to change back into the automatic mode of the control system. If the road milling machine continued milling during changing of the sensor, faults in the work result could occur because no control is effected during that time. The machine therefore needs to be stopped for a change of the sensor, which leads to a significant time loss. An adverse effect on the work result ensues even if the road milling machine is stopped during change of the sensor because the milling drum cuts clear when standing. This is an unwelcome effect, in particular during fine milling.
It is therefore the object of the invention to specify a road construction machine, as well as a leveling device and a method for controlling the milling depth and/or the milling slope, in which it is possible to change the sensors without any interruption of the milling operation.